Uterine leiomyoma is the most common tumor in women and causes severe morbidity in 15 to 30% of reproductive-age women. Epidemiological studies consistently indicate a correlation between leiomyoma development and exposure to endocrine-disrupting chemical phthalates, especially di-(2-ethylhexyl) phthalate (DEHP); however, the underlying mechanisms are unknown. Here, among the most commonly encountered phthalate metabolites, we found the strongest association between the urine levels of mono(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), the principal DEHP metabolite, and the risk of uterine leiomyoma diagnosis ( n = 712 patients). The treatment of primary leiomyoma and smooth muscle cells ( n = 29) with various mixtures of phthalate metabolites, at concentrations equivalent to those detected in urine samples, significantly increased cell viability and decreased apoptosis. MEHHP had the strongest effects on both cell viability and apoptosis. MEHHP increased cellular tryptophan and kynurenine levels strikingly and induced the expression of the tryptophan transporters SLC7A5 and SLC7A8, as well as, tryptophan 2,3-dioxygenase (TDO2), the key enzyme catalyzing the conversion of tryptophan to kynurenine that is the endogenous ligand of aryl hydrocarbon receptor (AHR). MEHHP stimulated nuclear localization of AHR and up-regulated the expression of CYP1A1 and CYP1B1, two prototype targets of AHR. siRNA knockdown or pharmacological inhibition of SLC7A5/SLC7A8, TDO2, or AHR abolished MEHHP-mediated effects on leiomyoma cell survival. These findings indicate that MEHHP promotes leiomyoma cell survival by activating the tryptophan-kynurenine-AHR pathway. This study pinpoints MEHHP exposure as a high-risk factor for leiomyoma growth, uncovers a mechanism by which exposure to environmental phthalate impacts leiomyoma pathogenesis, and may lead to the development of novel druggable targets.

Uterine fibroids (leiomyomas), the most common tumors in women and those assigned female at birth, originate from myometrial smooth muscle cells and cause heavy menstrual bleeding, anemia, pelvic discomfort, pregnancy loss, and obstruction of labor in approximately a quarter of reproductive-age women. During each ovulatory cycle, the myometrium responds to the ovarian steroids, estradiol, and progesterone, via increased tissue stem cell proliferation to prepare for impending pregnancy, during which a somatic mutation may arise to initiate a tumor. Both the mutated smooth muscle cells and the adjacent tumor-associated fibroblasts lay down excessive quantities of extracellular matrix, providing a unique feature that led to naming these tumors “fibroids.” The most common somatic mutations in fibroids affect the Mediator complex subunit 12 ( MED12; 77%) and high-mobility group AT-hook 2/1 ( HMGA2/1; 10%) genes. Heterozygous mutations in MED12, a chromatin-associated protein, disrupt the attached CDK8 kinase module in the Mediator complex. MED12 mutations are associated with increased genomic instability, altered chromatin landscape and enhancer engagement, and increased responsiveness to progesterone. Progesterone and a small stem cell population in a fibroid are essential for tumor survival and growth. Progesterone, via its receptors in differentiated fibroid cell populations, activates the production of Wingless-type MMTV integration site family (WNT) ligands, cytokines, and other growth substances to act on adjacent stem cells in a paracrine fashion to support tumor growth. Suppression of estrogen or progesterone production and progesterone antagonists have been used for temporary shrinkage of these tumors and symptom relief. Here we provide an overview of these mechanisms and future approaches for prevention and medical management of uterine fibroids.

Embryo implantation in the uterus is an essential process for successful pregnancy in mammals. In general, the endocrine system induces sufficient embryo receptivity in the endometrium, where adhesion-promoting molecules increase and adhesion-inhibitory molecules decrease. Although the precise mechanisms remain unknown, it is widely accepted that maternal–embryo communications, including embryonic signals, improve the receptive ability of the sex steroid hormone-primed endometrium. The embryo may utilize repulsive forces produced by an Eph–ephrin system for its timely attachment to and subsequent invasion through the endometrial epithelial layer. Importantly, the embryonic signals are considered to act on maternal immune cells to induce immune tolerance. They also elicit local inflammation that promotes endometrial differentiation and maternal tissue remodeling during embryo implantation and placentation. Additional clarification of the immune control mechanisms by embryonic signals, such as human chorionic gonadotropin, pre-implantation factor, zona pellucida degradation products, and laeverin, will aid in the further development of immunotherapy to minimize implantation failure in the future.

The circadian rhythm, which is necessary for reproduction, is controlled by clock genes. In the mouse uterus, the oscillation of the circadian clock gene has been observed. The transcription of the core clock gene period (Per) and cryptochrome (Cry) is activated by the heterodimer of the transcription factor circadian locomotor output cycles kaput (Clock) and brain and muscle Arnt-like protein-1 (Bmal1). By binding to E-box sequences in the promoters of Per1/2 and Cry1/2 genes, the CLOCK-BMAL1 heterodimer promotes the transcription of these genes. Per1/2 and Cry1/2 form a complex with the Clock/Bmal1 heterodimer and inactivate its transcriptional activities. Endometrial BMAL1 expression levels are lower in human recurrent-miscarriage sufferers. Additionally, it was shown that the presence of BMAL1-depleted decidual cells prevents trophoblast invasion, highlighting the importance of the endometrial clock throughout pregnancy. It is widely known that hormone synthesis is disturbed and sterility develops in Bmal1-deficient mice. Recently, we discovered that animals with uterus-specific Bmal1 loss also had poor placental development, and these mice also had intrauterine fetal death. Furthermore, it was shown that time-restricted feeding controlled the uterine clock’s circadian rhythm. The uterine clock system may be a possibility for pregnancy complications, according to these results. We summarize the most recent research on the close connection between the circadian clock and reproduction in this review.

Uterine leiomyomas cause heavy menstrual bleeding, anemia, and pregnancy loss in millions of women worldwide. Driver mutations in the transcriptional mediator complex subunit 12 (MED12) gene in uterine myometrial cells initiate 70% of leiomyomas that grow in a progesterone-dependent manner. We showed a distinct chromatin occupancy landscape of MED12 in mutant MED12 (mut-MED12) versus WT-MED12 leiomyomas. Integration of cistromic and transcriptomics data identified tryptophan 2,3-dioxygenase (TDO2) as the top mut-MED12 target gene that was significantly upregulated in mut-MED12 leiomyomas when compared with adjacent myometrium and WT-MED12 leiomyomas. TDO2 catalyzes the conversion of tryptophan to kynurenine, an aryl hydrocarbon receptor (AHR) ligand that we confirmed to be significantly elevated in mut-MED12 leiomyomas. Treatment of primary mut-MED12 leiomyoma cells with tryptophan or kynurenine stimulated AHR nuclear translocation, increased proliferation, inhibited apoptosis, and induced AHR-target gene expression, whereas blocking the TDO2/kynurenine/AHR pathway by siRNA or pharmacological treatment abolished these effects. Progesterone receptors regulated the expression of AHR and its target genes. In vivo, TDO2 expression positively correlated with the expression of genes crucial for leiomyoma growth. In summary, activation of the TDO2/kynurenine/AHR pathway selectively in mut-MED12 leiomyomas promoted tumor growth and may inform the future development of targeted treatments and precision medicine.

Inadequate dietary habits in youth are known to increase the risk of onset of various diseases in adulthood. Previously, we found that female college students who skipped breakfast had higher incidences of dysmenorrhea, suggesting that breakfast skipping interferes with ovarian and uterine functions. Since dietary habits can be managed by education, it is preferable to establish a convenient screening system for meal skipping that is associated with dysmenorrhea as part of routine services of health service centers. In this study, we recruited 3172 female students aged from 18 to 25 at Kanazawa University and carried out an annual survey of the status of students’ health and lifestyle in 2019, by a questionnaire. We obtained complete responses from 3110 students and analyzed the relationship between dietary habits, such as meal skipping and history of dieting, and menstrual disorders, such as troubles or worries with menstruation, menstrual irregularity, menstrual pain, and use of oral contraceptives. The incidence of troubles or worries with menstruation was significantly higher in those with breakfast skipping (p < 0.05) and a history of dieting (p < 0.001). This survey successfully confirmed the positive relationship between breakfast skipping and menstrual pain (p < 0.001), indicating that this simple screening test is suitable for picking up breakfast skippers who are more prone to gynecologic disorders. In conclusions, since dysmenorrhea is one of the important clinical signs, breakfast skipping may become an effective marker to predict the subsequent onset of gynecological diseases at health service centers. Considering educational correction of meal skipping, breakfast skipping is a potential and preventable predictor that will contribute to managing menstrual disorders from a preventive standpoint in the future.